Keyboard mapping (any)

I work with a lot of accountants and bookkeepers who find that the Windows convention of using the tab key to move between fields is very awkward (since it requires the use of both hands, one on the number pad and one for the tab key). They would like to find a way to map either the "+" key on the keypad or the Return key on the keypad to the Tab key. Then they could use one hand for data entry (like a desk calculator).

Has any one either seen such a keyboard defined for Windows or does someone in the forum know how to define an alternative keyboard like this?